After you confirm you have v3 BL,download this downgrade sbf from attachment and use RSD to flash it to your phone.Once you have done,you will have the new chinese 45.1.5 gb kernel(your BL is still 3,because this version can never be downgraded).Note!If you just want to use MIUI/CM7 based on froyo kernel, the downgrade job is already done here and you don't need to do the following steps. What you need to is just following the installation tuturial of MIUI/CM7).
Because the bootloader also check version of /system(CG39).so the original steps would not work.
Now,you already have the ability to flash the lower version sbf or said BL=2 sbf generally.But the sbf itself need to modified a bit. Download MotoAndroidDepacker from attachment and follow the following step:
2.click "Open from file" and select the sbf
3.click "Split to folder" and wait for it to finish
4.open the created folder and delete CG31.smg
5.back to MotoAndroidDepacker
6.click "Open files folder" and select the created folder
7.click "Compile file" and wait for it to finish
8.now,you will get a firmware.sbf in the created folder
Now you can use RSD to flash this sbf and get a clean and complete ROM,which could be official froyo or Chinese old gingerbread 45.1.3.
1.read the steps above and know how to edit sbf
2.find an nandroid backup of froyo system
3.restore it via clockwork recovery
4.open an froyo sbf and remove CG31/CG39 and repack it
5.flash it via RSD
6.reboot your phone
Now you will go back to froyo again.
Why it works:
Recently, China Moto release a new sbf for milestone2: 2.3.4-4.5.3-109_MS2-5-111219
the CG31/BL version of this sbf is also 3 but the key point is this new CG31/BL also contains signatures for older kernels( all froyo kernels&chinese gingerbread kernels ). If you don't want to download the whole sbf, the cg31,also cg35/61 are contained in the downgrade sbf.